(1) Field of the Invention
The present invention relates to a method of separating a semiconductor wafer held by being joined to a supporting member such as a glass plate via a double-faced adhesive sheet from the supporting member, and to a separating apparatus using the method.
(2) Description of the Related Art
Generally, a semiconductor wafer is subjected to a process of forming a number of devices on the surface of the semiconductor wafer. After that, in a back grind process, the back face of the semiconductor wafer is ground or polished to a desired thickness. The resultant semiconductor wafer is diced into devices in a dicing process.
In resent years, with rapid progress of an application, reduction in thickness of a semiconductor wafer to 100 μm to 50 μm, in some occasions, even to 25 μm is demanded. Such a thin semiconductor wafer is brittle and easily distorted and its handling is extremely difficult. Consequently, the semiconductor wafer is held by being joined to the surface side of a supporting member having strength such as a glass plate via a both-faced adhesive sheet. After the semiconductor wafer is reinforced by backing with the supporting member as described above, the back grind process is performed on the back face of the semiconductor wafer, and the semiconductor wafer is separated from the supporting member.
Hitherto, means for separating a semiconductor wafer held by being joined to a supporting member via a both-faced adhesive sheet is performed as follows. A both-faced adhesive sheet of an ultraviolet curing type whose adhesive strength is weakened by irradiation with an ultraviolet ray is used. First, by irradiation with ultraviolet rays, the adhesive strength is preliminarily decreased. In the subsequent process, the semiconductor wafer is sandwiched by upper and lower two tables and heated in a vacuumed state so as to be shrink-deformed, thereby reducing the contact area between the both-faced adhesive sheet and the semiconductor wafer, and the semiconductor wafer is floated.
After completion of the shrinking and separation of the both-faced adhesive sheet, suction of the upper table is cancelled and the upper table is withdrawn to the upper side. After that, in a state where the semiconductor wafer is suction-fixed on the lower table, a holding member is sucked and moved by a transport arm, thereby separating the semiconductor wafer from the both-faced adhesive sheet. Such means is proposed and carried out (see, for example, JP-A 2001-7179).
As the both-faced adhesive sheet used, not only a both-faced adhesive sheet of the ultraviolet curing type but also a both-faced adhesive sheet having heating separability which foams when heated and whose adhesive strength decreases are used.
The conventional means has the following problems.
First, when a semiconductor wafer is sandwiched and suction-held, an almost vacuum state is obtained in the space. Therefore, after separating of the both-faced adhesive sheet is determined, when suction of the upper table is cancelled and the upper table is withdrawn to the upper side, the contact faces of the supporting member and the upper table are in a nearly vacuum state, so that negative pressure is generated on the contact faces of both of the members. It causes a problem of occurrence of a warp in the semiconductor wafer.
Second, the distribution of the adhesive strength largely varies according to conditions such as the degree of shrink deformation of the both-faced adhesive sheet, the degree of ultraviolet curing, and the like. When the semiconductor wafer which is suction-fixed on the lower table is lifted and moved by forcefully suction-holding the supporting member, local separating stress acts on the semiconductor wafer, and there is a possibility in that a warp or breakage occurs.